1. Field of the Invention
The present invention generally relates to wiring, such as fuses, in semiconductor devices such as dynamic random access memories (DRAMs) and, more specifically, to fuses which can be opened using lower voltages and currents.
2. Description of the Related Art
Dynamic random access memory (DRAM) development technology has recently moved past 256 Mb to 1 Gb. Other technologies are similarly increasing the size of components and the density of components on a given semiconductor chip.
The increase in density on a given chip and the increase in chip size increases the chance of defects within a given product. Therefore, it is very important to include redundant components which can be easily substituted for defective components, using selectively blowable fuses. While some redundancy repair techniques only allow wafer level repair, electrically blowable fuses allow redundant modules within a wafer to replace defective modules on the same wafer.
The key elements important in producing robust and viable electric fuses include ease of use, ability to fabricate the fuse using existing processes and the ability to reliably use a laser to selectively open the fuses. One of the most important parameters in determining the efficiency of an electrical fuse design is the amount of effort it takes to blow ("delete" or "open") the fuse and maintain the open condition during the fuse's operating life.
Creating a fuse link with a high resistance and increased current density allows the fuse to be blown more easily for a constant input current. Resistive heating generally causes the fuse link material to melt, causes a phase change of the fuse material to a non-conductive state, or causes the fuse material to move away from the fuse link location to prevent the possibility of continued conduction through a blown fuse.
The invention increases the performance of such fuses through a simplified method of forming fuses which are very small (having sub-lithographic feature sizes) and which, therefore, have increased current density.